java.sql
Interface SQLData

public interface SQLData

An interface for the custom mapping of an SQL User Defined Type (UDT) to a Java Class. The Java Class object will be added to the Connection's type map with the SQL Name of the UDT which it maps.

Usually within an implementation of SQLData, there is a corresponding field for every attribute of an SQL type, or only one field if the type is SQL DISTINCT. When the UDT is returned within a ResultSet, it is accessed with the ResultSet.getObject method and is returned as an Object which is an instance of the class defined by the SQLData mapping. The application can use this object just like any other Java object and can store changes back into the database using the PreparedStatement.setObject method which performs the reverse mapping into the SQL UDT.

It is standard for an implementation for a custom mapping to be generated by a tool. The tool usually requires the name of the SQL UDT, the name of the class which it is going to be mapped to, and the field names to which the UDT attributes will be mapped. The tool can then implement the SQLData readSQL and writeSQL methods. readSQL reads attributes from an SQLInput object, and writeSQL writes them. This is done via SQLInput and SQLOutput method calls respectively

Ordinarily a programmer would not call SQLData methods directly. Similarly SQLInput and SQLOutput methods are not usually called directly.

Method Summary

String	getSQLTypeName() Gets the SQL name of the User Defined Type (UDT) that this object represents.
void	readSQL(SQLInput stream, String typeName) Reads data from the database into this object.
void	writeSQL(SQLOutput stream) Writes the object to a supplied SQLOutput data stream, writing it out as an SQL value to the data source.

Method Detail

getSQLTypeName

String getSQLTypeName()
                      throws SQLException

Gets the SQL name of the User Defined Type (UDT) that this object represents. This method, usually invoked by the JDBC driver, retrieves the name of the UDT instance associated with this SQLData object.

Returns:

a string with UDT type name for this object mapping, passed to readSQL when the object was created

Throws:

SQLException - if a database error occurs

readSQL

void readSQL(SQLInput stream,
             String typeName)
             throws SQLException

Reads data from the database into this object. This method follows these steps:

• Utilize the passed input stream to read the attributes or entries of the SQL type
• This is carried out by reading each entry from the input stream, ordered as the are the SQL definition.
• Assign the data to the appropriate fields or elements. This is done by calling the relevant reader method for the type involved (eg. SQLInput.readString, SQLInputreadBigDecimal). If the type is distinct, then read its only data entry. For structured types, read every entry.

The supplied input stream is typically initialized by the calling JDBC driver with the type map before readSQL is called.

Parameters:

stream - the SQLInput stream from which the type map data is read for the custom mapping

typeName - the SQL Type name for the type which is being mapped

Throws:

SQLException - if a database error occurs

writeSQL

void writeSQL(SQLOutput stream)
              throws SQLException

Writes the object to a supplied SQLOutput data stream, writing it out as an SQL value to the data source.

This method follows the following steps:

• Write each attribute of the SQL type to the output stream.
• Write each item by calling a method on the output stream, in the order they appear in the SQL definition of the type. Use the appropriate SQLOutput methods (eg. writeInt, writeString). Write a single data element for a Distinct type. For a Structured type, write a value for each attribute of the the SQL type.

Parameters:

stream - the SQLOutput stream to use to write out the data for the custom mapping

Throws:

SQLException - if a database error occurs